Intracellular imaging and targeted delivery demand new nanomaterials that can directly cross cell membranes and enter the cytosol without being encapsulated by membrane bound vesicles. We recently found that highly luminescent, gold nanoparticles about 2 nm in diameter when exposed to HeLa cells rapidly crossed cellular membranes and nuclear membranes apparently by passive diffusion and subsequently bound to chromosomes in live cells. The objective of this application is to unravel underlying principles that govern the cell/nuclear permeability of nanomaterials. To achieve this goal, we proposed to develop general approaches that allow us to create a library of gold nanoprobes with fine tuned surface chemistry and structure, and then apply fluorescence microscopy techniques to investigate cell behaviors of these nanomaterials. Successful realization of these aims will greatly advance our understanding of fundamental principles that regulate the permeability of nanostructures at the molecular level. These studies will be further broadened beyond the scope of this exploratory period and lead to development of new nanomedicines for intracellular imaging and targeted delivery. PUBLIC HEALTH RELEVANCE: Cell- and Nucleus-Permeable Luminescent Gold Nanoparticles Nanomaterials generally cannot cross cell /nuclear membranes via passive diffusion, but are taken up by the cell via endocytosis. We recently found a luminescent gold nanostructure can directly diffuse across cell and nuclear membranes within a few minutes. We propose to develop a library of luminescent gold nanoprobes with different surface properties, so that we can uncover the underlying principles that govern cell and nuclear permeability of gold nanoparticles. 1